1. Field of the Invention (Technical Field)
The present invention relates to selective modification of rheological properties of foodstuffs to enhance processing. More specifically, the present invention enhances tree nutshell fracturing processes by contacting tree nuts with a cryogen.
2. Background Art
Food processing generally adds value to raw or commodity foodstuffs. Often raw foodstuffs must be ground, milled, fractured or crushed to produce a final marketable product. Rheological properties of foodstuffs govern the selection and ultimately the efficiency of such processes. Rheological properties determine how materials flow or deform. For instance, hydration typically reduces the Young's modulus (a parameter used to help characterize the relationship between stress and strain) and yield stress of foodstuffs like starch grains. A reduced Young's modulus corresponds to an increase in strain for a given amount of applied stress whereas a reduced yield stress means that the foodstuff will fracture or shear at a reduced applied stress. High levels of hydration may minimize or even eliminate fracturing, in such instances, the yield stress corresponds to shearing or the point where the applied stress causes the foodstuff to flow. Other processes such as freezing affect the rheological properties of foodstuffs differently. Freezing usually increases the Young's modulus; however, the yield stress may increase or decrease depending on the physical structure of the foodstuff. In the case of foodstuffs with a substantial water activity, the time-temperature curve, i.e., the rate of cooling, often determines crystal size. For example, slow freezing produces larger crystals whereas rapid freezing produces smaller crystals, Furthermore, slow freezing segregates soluble materials more so than rapid freezing. Although frozen foodstuffs almost always have a higher Young's modulus, those with larger crystals frequently fracture differently than those with smaller crystals. To facilitate fracturing, a high Young's modulus and a lower yield stress are desirable.
The following U.S. Patents disclose methods for cooling foodstuffs using cryogens: U.S. Pat. No. 5,333,802, entitled "Method and apparatus for producing chunks or kibbles of a foodstuff," to Seelig et al., discloses use of a liquid cryogen to alter rheological properties of foodstuffs prior to chunking or kibbling. U.S. Pat. No. 4,742,686, entitled "Process for increasing tree nut shelling efficiency," to Cook, discloses use of a cryogen to freeze tree nuts whereby nut kernals become harder than nutshells. U.S. Pat. No. 4,436,757, entitled "Cryogenic process for decortication and hulling of sunflower seeds," to Lange et al., discloses use of cryogen diffusion into sunflower seeds followed by rapid heating to cause gas expansion and hull separation. U.S. Pat. No. 4,177,296. entitled "Process for the preparation of peanut-curd." to Mochizuki et al., discloses cryogenic cooling and pulverizing of pressed peanuts to obtain a peanut-curd. U.S. Pat. No. 4,004,037, entitled "Peanut butter manufacture," to Connick, discloses use of cryogens for preparation of peanut butter in a non-oxidizing, low-temperature environment. U.S. Pat. No. 3,452,936, entitled "Reduction of cereal grains to flour," to Hanser, discloses use of cryogenic conditions for processing cereal grains. U.S. Pat. No. 3,413,818, entitled "Immersion freezing," to Pelmulder, discloses cyrogenic processing of foodstuffs for storage or for subsequent freeze-drying. U.S. Pat. No. 3,214,928, entitled "Method and apparatus for freezing food products," to Oberdorfer, discloses spraying and showering of cryogenic fluids for freezing food products.